A field programmable gate array (FPGA) is a type of integrated circuit consisting of an array of programmable logic blocks interconnected by programmable routing resources and programmable I/O cells. Programming of these logic blocks, routing resources and I/O cells is selectively completed to make the necessary interconnections that establish a configuration thereof to provide desired system operation/function for a particular circuit application.
Of course, it is desirable to complete diagnostic testing of all types of integrated circuits including FPGAs in order to check the functionality of the various programmable logic blocks, routing resources and I/O cells of the FPGAs. Since FPGAs are programmable, however, the diagnostic testing thereof is complicated by the need to cover all possible modes of operation and even many non-classical fault models (faults effecting the programmable interconnect network, delay faults, etc.).
In past diagnostic testing approaches, special test transistors and circuits have been added to each FPGA integrated circuit. These additional test transistors and circuits increase the complexity and space requirements or "area overhead" of the FPGAs. In fact, the size of the FPGAs is typically increased between 10-30% in order to accommodate the built-in test circuitry and significant delay penalties in the operating speed of the FPGAs result.
It should further be noted that in current state of the art testing procedures, tests are generated manually by configuring the FPGAs into several application circuits. The FPGAs so configured are then exercised with test vectors developed specifically for each application circuit. Since these circuits all share the same set of faults, FPGAs are rejected even if a fault is detected in only one of their circuits.
While this is an effective testing procedure, it does suffer from a number of drawbacks. For example, since all the application circuits must be simulated to complete testing for stuck-at faults, fault simulation in accordance with this procedure is very expensive. Additionally, the tests require a significant amount of time to complete and relatively sophisticated and expensive automatic test equipment (ATE) must be utilized.
Further, it should be appreciated that the FPGA manufacturing tests presently utilized are not reusable for board and system-level testing. Hence, additional developmental effort is required in order to complete a testing procedure at the system-level. The state of the art approach to system-level testing of FPGAs focuses upon the development of off-line system diagnostic routines to test the FPGAs in the system mode of operation. The development of these routines is costly and time consuming. This, of course, is another significant drawback to state of the art FPGA diagnostic testing.
A need is therefore identified for an improved approach for completing diagnostic testing of FPGAs.